1. Field of the Invention
The present invention relates to extrudable multiphase liquid cleansing compositions of the type typically used in skin cleansing or shower gel compositions which compositions are xe2x80x9cstructuredxe2x80x9d lamellar phase compositions.
2. Background of the Invention
Compositions which both provide a cleansing function and a moisturizing benefit are known. For example, WO 90/13283 to Green, et al., published on Nov. 15, 1990; included herein by reference, discloses compositions comprising an acyl ester of an isethionic acid salt, a long chain fatty acid, a moisturizer component and optional soap.
One problem which had been previously encountered with such dual purpose compositions is that they contain an insufficient level of moisturizer component; or an insufficient amount deposits on use.
Another problem associated with such dual cleansing and moisturizing compositions is instability. According to WO 94/03152 to Helliwell, published on Feb. 17, 1994; included herein by reference, concerned with shower gels comprising a non-soap detergent, silicone oil and cationic polymers, the maximum average droplet size of the silicone oil that can be used is 2 microns, if product stability is to be maintained.
In applicants U.S. Pat. No. 5,612,307 issued to Chambers, et al., on Mar. 18, 1997, included herein by reference, applicants found that enhanced deposition of benefit agent could be obtained in a stable formulation by using a dual cleansing and moisturizing product in which the cleansing and moisturizing components were separately, but combinedly dispensed from a packaging means as discrete domains/stripes.
More specifically, the compositions of Chambers, et al. comprised a surfactant containing base formulation and a benefit agent wherein the benefit agent and base formulation were physically separate (not in direct contact) but were nonetheless dispensable from a single packaging means comprising both the base formulation and benefit agent as individual stripes. The stripes had width of at least 1000 microns and base formulation and benefit agent stripes were not post mixed prior to use (compared to EP 468,703 to Unilever where post-mixing is required).
In applicants U.S. Pat. No. 5,929,019 issued to Puvvada et al., on Jul. 27, 1999; included herein by reference, applicants found that the same separately dispensed, non-mixed prior to use, dual cleanser/moisturizer compositions described by Chambers, et al., except that the benefit agent stripe had been modified so that it now may include surfactant.
Multiphase cleansing and cosmetic compositions which are not segregated in their package are also known. For example, in U.S. Pat. No. 5,059,414 issued to Dallal et al. on Oct. 22, 1991; included herein by reference, a multi-phase high viscosity cosmetic product containing two or more independent products in single container, along with simultaneous dispensing, is described. However, Dallal describes isotropic products for the hair, whereas the present invention relates to lamellar liquids for personal care (hand, body and hair).
In another example, WO 9824399 to Bordat et al., published on Jun. 11, 1998; included herein by reference, describes highly viscous, separate aqueous and oil phase emulsion compositions squeezed out together as single strand from tube dispenser for use with the skin, body or hair. In comparison, the present invention uses lamellar liquids with low shear viscosity values between 80-300 K cps.
The rheological behavior of all surfactant solutions, including liquid cleansing solutions, is strongly dependent on the microstructure, i.e., the shape and concentration of micelles or other self-assembled structures in solution.
When there is sufficient surfactant to form micelles (concentrations above the critical micelle concentration or CMC), for example, spherical, cylindrical (rod-like) or discoidal micelles may form. As surfactant concentration increases, ordered liquid crystalline phases such as lamellar phase, hexagonal phase or cubic phase may form. The lamellar phase, for example, consists of alternating surfactant bilayers and water layers. These layers are not generally flat but fold to form submicron spherical onion like structures called vesicles or liposomes. The hexagonal phase, on the other hand, consists of long cylindrical micelles arranged in a hexagonal lattice. In general, the microstructure of most personal care products consist of either spherical micelles; rod micelles; or a lamellar dispersion.
As noted above, micelles may be spherical or rod-like. Formulations having spherical micelles tend to have a low viscosity and exhibit Newtonian shear behavior (i.e., viscosity stays constant as a function of shear rate; thus, if easy pouring of product is desired, the solution is less viscous and, as a consequence, it doesn""t suspend as well). In these systems, the viscosity increases linearly with surfactant concentration.
Rod micellar solutions are more viscous because movement of the longer micelles is restricted. At a critical shear rate, the micelles align and the solution becomes shear thinning. Addition of salts increases the size of the rod micelles thereof increasing zero shear viscosity (i.e., viscosity when sitting in bottle) which helps suspend particles but also increases critical shear rate (point at which product becomes shear thinning; higher critical shear rates means product is more difficult to pour).
Lamellar dispersions differ from both spherical and rod-like micelles because they can have high zero shear viscosity (because of the close packed arrangement of constituent lamellar droplets), yet these solutions are very shear thinning (readily dispense on pouring). That is, the solutions can become thinner than rod micellar solutions at moderate shear rates.
In formulating liquid cleansing compositions, therefore, there is the choice of using rod-micellar solutions (whose zero shear viscosity, e.g., suspending ability, is not very good and/or are not very shear thinning); or lamellar dispersions (with higher zero shear viscosity, e.g. better suspending, and yet are very shear thinning). Such lamellar compositions are characterized by high zero shear viscosity (good for suspending and/or structuring) while simultaneously being very shear thinning such that they readily dispense in pouring. Such compositions possess a xe2x80x9cheapingxe2x80x9d, lotion-like appearance which convey signals of enhanced moisturization.
To form such lamellar compositions, however, some compromises have to be made. First, generally higher amounts of surfactant are required to form the lamellar phase. Thus, it is often needed to add auxiliary surfactants and/or salts which are neither desirable nor needed. Second, only certain surfactants will form this phase and, therefore, the choice of surfactants is restricted.
In short, lamellar compositions are generally more desirable (especially for suspending emollient and for providing consumer aesthetics), but more expensive in that they generally require more surfactant and are more restricted in the range of surfactants that can be used.
When rod-micellar solutions are used, they also often require the use of external structurants to enhance viscosity and to suspend particles (again, because they have lower zero shear viscosity than lamellar phase solutions). For this, carbomers and clays are often used. At higher shear rates (as in product dispensing, application of product to body, or rubbing with hands), since the rod-micellar solutions are less shear thinning, the viscosity of the solution stays high and the product can be stringy and thick. Lamellar dispersion based products, having higher zero shear viscosity, can more readily suspend emollients and are typically more creamy. Again, however, they are generally more expensive to make (e.g., they are restricted as to which surfactants can be used and often require greater concentration of surfactants).
In general, lamellar phase compositions are easy to identify by their characteristic focal conic shape and oily streak texture while hexagonal phase exhibits angular fan-like texture. In contrast, micellar phases are optically isotropic.
It should be understood that lamellar phases may be formed in a wide variety of surfactant systems using a wide variety of lamellar phase xe2x80x9cinducersxe2x80x9d as described, for example, in U.S. Pat. No. 5,952,286 issued to Puvvada, et al., on Sep. 14, 1999. Generally, the transition from micelle to lamellar phase are functions of effective average area of headgroup of the surfactant, the length of the extended tail, and the volume of tail. Using branched surfactants or surfactants with smaller headgroups or bulky tails are also effective ways of inducing transitions from rod micellar to lamellar.
One way of characterizing lamellar dispersions include measuring viscosity at low shear rate (using for example a Stress Rheometer) when additional inducer (e.g., oleic acid or isostearic acid) is used. At higher amounts of inducer, the low shear viscosity will significantly increase.
Another way of measuring lamellar dispersions is using freeze fracture electron microscopy. Micrographs generally will show lamellar microstructure and close packed organization of the lamellar droplets (generally in size range of about 2 microns).
Applicants have discovered that a stable, extrudable multiphase product can be prepared. The term multiphase product is here defined as the combination of two or more distinct lamellar compositions having viscosities of at least about 80,000 cps (T-bar) at 25xc2x0 C. Preferably the viscosity has an upper limit of 300,000 cps at 25xc2x0 C. in order to facilitate filling containers and dispensing with a conventional pump bottle. The lamellar phases may have substantially the same or different compositions, but preferably the phases have similar rheological properties, such as viscosity, etc. The lamellar phases preferably have different colors or other visual differences and preferably are filled vertically or in a pulsating manner in a single container without any partitions, i.e. xe2x80x9cpartitionlessxe2x80x9d.
Squeezing a flexible container holding the inventive product may dispense the product but a single pump, or the like, is preferably used to dispense the product. When dispensed, each phase of the multiphase inventive product should be present in the concentration range of 1-99 weight %. In this manner, duality in the case of a two phase system, can be advantageously, economically, and visually communicated through a single, partitionless container. Another advantage of the inventive product is the fact that two or more separate lamellar compositions having specific functions, e.g. cleansing and moisturizing the skin may be simultaneously dispensed in a partitionless container. A further advantage of using a lamellar composition is that elevated amounts of emollients can be added to the formula without affecting product stability. Unexpectedly, the lamellar phases in the inventive product remain separated (i.e. do not mix) at room temperature for at least 4 months and at high temperature (125xc2x0 F.) for at least two weeks. xe2x80x9cStabilityxe2x80x9d is therefore defined as used herein as the ability of the multiphase lamellar product to maintain the separation of each phase from the other under this combination of time and temperature.
In accordance with these and other aspects of the invention, the invention will now be described with reference to the accompanying drawing.